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Author Topic: AL-811H high plate current  (Read 1630 times)
N8EUI
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Posts: 146




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« on: October 24, 2012, 10:04:07 PM »

Hello everyone,

I purchased an Ameritron AL-811H amp. Per the tuning up instructions in the operator's manual on page 6, the plate current with no exciter drive should be 125 ma. My meter is indicating 175-180ma. Should I be concerned about this? I have the amp set for 240 volt operation. My line voltage reads about 241 volts. Other than this, the '811H still loads up per the operator manual.

Thank you,
Tom, N8EUI
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G4LNA
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Posts: 26




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« Reply #1 on: October 25, 2012, 05:10:41 AM »

Sorry, I was looking at the wrong specification for those tubes, so I've deleted my comments rather than lead you astray.
« Last Edit: October 25, 2012, 05:14:30 AM by G4LNA » Logged
G4LNA
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« Reply #2 on: October 25, 2012, 05:24:05 AM »

Let's start again, for four tubes the max allowable dissipation is 260W at 1500V so with 125ma the tubes are within spec at 187.5W but with 175ma the total dissipation is 262.5W which puts the tubes slightly above their rated dissipation, so yes, I would say it is a bit high.

I have had a look at the manual and are you sure the tappings are correct? 241V should not make that much difference, if your line voltage is the same spec as ours it is plus or minus 10% of the nominal or declared voltage anyway.
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WX7G
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« Reply #3 on: October 25, 2012, 06:24:50 AM »

You can look at the tube plates and see if they are all about the same color. At rated 65 watts dissipation they should be a dull red color.
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W8JI
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« Reply #4 on: October 25, 2012, 07:26:51 AM »

Hello everyone,

I purchased an Ameritron AL-811H amp. Per the tuning up instructions in the operator's manual on page 6, the plate current with no exciter drive should be 125 ma. My meter is indicating 175-180ma. Should I be concerned about this? I have the amp set for 240 volt operation. My line voltage reads about 241 volts. Other than this, the '811H still loads up per the operator manual.

Thank you,
Tom, N8EUI


What year was the amp made?

Tubes changed charateristics and started drawing more current. If it is an older amp without bias diodes, you might need to add about 3-4 volts of bias in the center tap lead. You can do that with a string of diodes.

Read this, especially 1, 2, and 4:

http://www.w8ji.com/ameritron_811h_572_amplifier_trouble_shooting.htm
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N8EUI
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« Reply #5 on: October 25, 2012, 07:51:53 AM »

Hello W8JI,

The amp was built in the early 2000's.  The serial number is AL-811H-19356.  It sat in a fellow ham's closet for a few years and was used very little.

Thanks,
Tom, N8EUI
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W8JI
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« Reply #6 on: October 27, 2012, 09:49:17 AM »

Hello W8JI,

The amp was built in the early 2000's.  The serial number is AL-811H-19356.  It sat in a fellow ham's closet for a few years and was used very little.

Thanks,
Tom, N8EUI

I probably does not have the diode bias.

I would add it.
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N8EUI
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Posts: 146




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« Reply #7 on: October 29, 2012, 11:15:16 AM »

Hi W8JI,

I'll open it up an take a look see.

Thanks,
Tom
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